Anomalous transport of microalgae Chlorella vulgaris in microfluidic channel / Nur Izzati Ishak

Nur Izzati , Ishak (2018) Anomalous transport of microalgae Chlorella vulgaris in microfluidic channel / Nur Izzati Ishak. Masters thesis, University of Malaya.

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Abstract

Transport phenomena occur in diverse natural and man-made processes, ranging from the diffusion of charge carriers in conductors, semiconductors, ion channels in biological systems, movement of the dust particles or microorganisms in media and data transport in communication networks. Normal diffusion is characterized by linear scaling of the mean square displacement (MSD) with respect to time and can be modelled using Brownian motion. Anomalous diffusion refers to deviation from this linear scaling law to follow MSD ~ tα, with scaling exponent α used to classify the transport dynamics, namely sub-diffusion when 0 < α <1 and super-diffusion when 1< α <2. This study examined the transport behavior of microalgae Chlorella vulgaris as particles through a microfluidic channel under different flow rate. The flow is controlled through a pressure driven system and the motion of the microalgae is observed using high-speed CCD video camera with suitable optical magnification. The particle trajectories were reconstructed from the recorded sequential images and the basic statistics and the MSDs were calculated. A numerical simulation of the particles transport in a microfluidic channel was carried using COMSOL Multiphysics software. For simplicity, the microalgae particles were treated as spherical naturally buoyant. In both microfluidic experiment and numerical simulation, scaling behavior of MSD, probability density function (PDF), and velocity autocorrelation (VCAF) of the particle were analyzed by resolving the displacement in the streamwise (flow) and perpendicular (wall-normal) directions. Regional variations of the flow characteristics at the near-walls and center regions of the channel were also investigated. The scaled Brownian motion (SBM) model with power-law MSD scaling and time-dependent diffusion coefficient was used to describe the MSD scaling behaviors. The results showed the presence of anisotropic anomalous transport in all the three flow regions with mixed sub-diffusive, normal and super-diffusive behavior in both longitudinal and transverse directions. Both experimental and numerical finding agreed on the transient scaling behaviors in the MSDs, but with different scaling exponent MSD. These findings are considered useful for optimizing the mixing process, the dispersion of the microalgae, and the flow implementation in the photobioreactor.

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